We propose to elucidate certain aspects of the interaction of somatostatin with rat pancreatic islets using the technique of electron microscopic autoradiography. This research will study the subcellular distribution and location of somatostatin receptors in alpha and beta cells of rat islets. In addition, we propose to examine the metabolism of somatostatin within the target cells using radioactively labeled somatostatin and subcellular fractionation. The effect of somatostatin upon subcellular organelles of alpha and beta cells will be examined using electron microscopy. The effect of time, Ca ions, and glucose on the location of labeled somatostatin within the alpha and beta cells will be followed both by autoradiography and by subcellular fractionation to determine the amounts of both intact and metabolized somatostatin.